The present invention relates to the field of antenna structures and more particularly to antenna structures and devices including at least two antennas.
Radiotelephone mobile terminals are being developed including multiple functionalities. For example, mobile terminals are being developed that will provide both radiotelephone communications as well as global positioning system (GPS) functions. When making an emergency (911) call, the mobile terminal could thus precisely determine its location, and transmit that location as a part of the emergency (911) call.
The addition of a GPS antenna and receiver to a mobile terminal may result in complications. First, the volume of a GPS antenna may be difficult to incorporate in a relatively small mobile terminal. In other words, it may be difficult to add a GPS antenna without increasing a size of the mobile terminal. Moreover, simply adding another antenna to the outside of the mobile terminal may be esthetically undesirable.
A second potential complication relates to isolation of the GPS antenna and the communications antenna. In a small mobile terminal, the GPS antenna and the communications antenna may need to coexist in close proximity. The resulting interference and/or coupling between the two antennas may degrade the performance of both global positioning and communications functionality. For example, a circuit coupled to one antenna may absorb power coupled to it from the other antenna thereby reducing efficiency of the other antenna. Alternately, a circuit coupled to one antenna may reflect power coupled from the other antenna thereby distorting a radiation pattern for the other antenna.
Isolation of 10 dB to 15 dB or higher may thus be desirable to acceptably reduce coupling and/or interference between the two antennas and to maintain both GPS and communications functionalities. While filters may be used to provide isolation between the antennas, filters may undesirably increase costs in terms of circuit board area, insertion loss, and component cost.